an Olde Boston Bulldogge! Bigger than what you are looking for, and hard to find (only 3 breeders on the continent that I am aware of), but an AMAZING animal- real big dog personality in a smaller size and very smart.

If not that, then a Boston terrier, French bulldog, or an English bulldog, even though bullies often snore, they are just way too awesome. Clean, calm, trustworthy when left alone, good with kids, and easy to train. I have a bigger bully breed and will never have another type of dog! They're perfect.

Here's pics of the Olde Boston... Olde Boston Bulldogge (Old Boston Bulldog) by Bulldog Information